title: Control of plant germline proliferation by SCF(FBL17) degradation of cell cycle inhibitors.
abstract: Flowering plants possess a unique reproductive strategy, involving double fertilization by twin sperm cells. Unlike animal germ lines, the male germ cell lineage in plants only forms after meiosis and involves asymmetric division of haploid microspores, to produce a large, non-germline vegetative cell and a germ cell that undergoes one further division to produce the twin sperm cells. Although this switch in cell cycle control is critical for sperm cell production and delivery, the underlying molecular mechanisms are unknown. Here we identify a novel F-box protein of Arabidopsis thaliana, designated FBL17 (F-box-like 17), that enables this switch by targeting the degradation of cyclin-dependent kinase A;1 inhibitors specifically in male germ cells. We show that FBL17 is transiently expressed in the male germ line after asymmetric division and forms an SKP1-Cullin1-F-box protein (SCF) E3 ubiquitin ligase complex (SCF(FBL17)) that targets the cyclin-dependent kinase inhibitors KRP6 and KRP7 for proteasome-dependent degradation. Accordingly, the loss of FBL17 function leads to the stabilization of KRP6 and inhibition of germ cell cycle progression. Our results identify SCF(FBL17) as an essential male germ cell proliferation complex that promotes twin sperm cell production and double fertilization in flowering plants.
authors.affiliation: Division of Molecular Life Sciences, Pohang University of Science and Technology, Pohang 790-784, South Korea.
authors.forename: Hyo Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Sung Aeong
authors.initials: SA
authors.lastname: Oh
authors.forename: Lynette
authors.initials: L
authors.lastname: Brownfield
authors.forename: Sung Hyun
authors.initials: SH
authors.lastname: Hong
authors.forename: Hojin
authors.initials: H
authors.lastname: Ryu
authors.forename: Ildoo
authors.initials: I
authors.lastname: Hwang
authors.forename: David
authors.initials: D
authors.lastname: Twell
authors.forename: Hong Gil
authors.initials: HG
authors.lastname: Nam
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division / Q000235:genetics; D049109:Cell Proliferation; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000378:metabolism*; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D009154:Mutation; D011058:Pollen / Q000166:cytology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism
chemical_list: C532796:AT3G54650 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D044783:F-Box Proteins; D044843:SKP Cullin F-Box Protein Ligases; D046988:Proteasome Endopeptidase Complex